stir plate help

[mthibodeau]

I assembled and tested my stir plate the other day and it seemed to work fine.

However it constantly throws the magnet, I have a pc fan speed controller hooked in line to control the voltage (really touchy but it seems to work), and for magnets im using 2 small rare earth magnets from Princess. The magnets seem balanced on the fan, it doesnt wobble or vibrate at all

any suggestions?

[mthibodeau]

to clarify, it throws the magnet generally just as a vortex is starting up

[mckay75]

What size stir bar are you using?

You may need stronger magnets on your fan. I'm using a stack of 3 x 1/2" magnets on each side (total of 6) of these on my homemade stir plate.

http://www.leevalley.com/en/wood/page.a ... 2363,42348" onclick="window.open(this.href);return false;

Still very temperamental...but that being said...I borrowed Pete's real stir plate last week and could not get it to work with a 2.5L starter in a 5L flask. It was doing the same thing you describe...throwing the stir bar once the vortex started. I ended up going back to my homemade stir plate. I'm thinking about getting some stronger magnets as well as a stronger stir bar to see if that helps any.

[mthibodeau]

thanks, thats probably my issue, im using one 8mm magnet on each side, ill try a stack and see how that goes

[mthibodeau]

that did it, thanks

[mthibodeau]

and now I think the potentiometer is dead. Where did anybody else get theirs? My cheap Chinese ebay purchase is dead

[mckay75]

I got mine from still dragon when I ordered my controller. It doesn't work great though...had 2 speeds...on and off...I can't control the speed whatsoever. Likely overkill for this build.

http://stilldragon.com/index.php/potentiometer.html" onclick="window.open(this.href);return false;

[RossBee]

I'm using a dimmer switch with a 120V computer/overhead projector fan, a 2" bar and two 1/2" rare earth magnets, all mounted on the bottom of a bucket.